The process of solution spinning involves dissolving a desired polymer into a suitable solvent, and spinning fibers from the polymer/solvent solution. Often, the solvent is an organic solvent which has undesirable properties in use of the so-formed fabric, such as adverse health effects, undesired odor and the like. It would be desirable to strip the unwanted solvent from the fibers or fabric during the production process, prior to shipping to the ultimate customer.
Solution spinning processes are frequently used to manufacture fibers and nonwoven fabrics, and in some cases have the advantage of high throughputs, such that the fibers or fabrics can be made in large, commercially viable quantities. Unfortunately, when solution spinning large quantities of fabric at high throughput through the spinning dies, significant quantities of residual solvent can be entrained in the collected fabrics or fibers. Ideally, the residual solvent would merely evaporate upon sitting, leaving the fabric solvent-free, but in many cases the ideal solvent used for the solution spinning process has a high chemical or physical affinity for the fiber polymer. In some cases, the fiber polymer is swollen by the solvent; i.e. the solvent is “dissolved” within the fiber polymer. In other cases the solvent chemically bonds to the fiber, such as by hydrogen bonding, Van der Waals forces, or even ionically via salt formation.
Further, in typical nonwoven fabric spinning processes, the fabric is spun and wound into a large roll in an essentially continuous operation, such that even if the solvent were amenable to evaporation upon sitting, only the solvent entrained in the fabric on the outside of the roll is effectively evaporated, since the underlying fabric within the roll is not exposed to the atmosphere. Detrimentally, even if the fabric were to be provided sufficient time in the unrolled state to permit the spinning solvent to evaporate, an exceedingly long area would be necessary to provide room for the unrolled fabric, and recovery of the evaporated solvent would be difficult and expensive.
In paper making processes, such as those disclosed in U.S. Pat. Nos. 3,503,134 and 6,986,830, dewatering of the wet laid cellulose fibers which form the paper is performed by passing the wet laid cellulose web over a vacuum-assisted porous drum, and the excess water from the forming process is drawn through and away from the paper web. U.S. Pat. No. 3,503,134 discloses the use of hot air, superheated steam or a steam-air mix to enhance the drying effect of the vacuum assist. U.S. Pat. No. 6,986,830 discloses positioning the wet laid paper web between two soft, porous cloth webs, wherein the porous cloths on either side of the paper web pull additional water from the paper by capillary action. However, in either case, while it is advantageous to remove as much water as possible from the wet laid paper web, residual water is non-toxic and would not cause adverse health effects if present in the finished product.
U.S. Published patent application No. 2002/0092423 discloses a solution spinning process for forming a nonwoven polymer web, in particular an electrospinning process, wherein polymeric microfibers or nanofibers are produced from a polymer solution exiting an electrically-charged rotating emitter and directed toward a grounded collector grid. However, according to the applicants thereof, the solvent is evaporated from the fibers “in flight” between the emitter and the collector grid. The throughput of the electrospinning process disclosed in U.S. Published patent application No. 2002/0092423 is relatively low at about 1.5 ml/min/emitter, and as such would form relatively light basis weight polymer webs.